Resonance in Optimal Perturbation Evolution. Part I: Two-Layer Eady Model
Resonance in Optimal Perturbation Evolution. Part I: Two-Layer Eady Model
复制标题
最优扰动演化中的共振。
DOI：
10.1175/jas3867.1
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发表时间：
2007
影响因子：
3.1
通讯作者：
J. D. Opsteegh
中科院分区：
文献类型：
--
作者：
H. Vries;J. D. Opsteegh
一个详细的调查已经进行了不同的增长机制（共振，位涡无屏蔽，和正常模式斜压不稳定性）的最佳扰动的演变构造的两层Eady模式和动能规范的作用。两层Eady模式是通过用一个简单但实际的平流层代替传统的刚性上盖而得到的。为了使一个明确的讨论可能，普遍适用的技术已经开发出来。在这些技术的核心在于一个变量的位涡构建块（PVBs），这是纬向波状，垂直本地化的位涡片的线性动力学的描述。如果最佳扰动仅由一个PVB组成，则快速的表面气旋生成可以归因于表面PVB（边缘波）的增长，该边缘波由对流层PVB通过线性共振效应激发。如果使用多个PVBs构建最佳扰动，则仅在初始化后的短时间内PV非屏蔽主导表面放大的意义上修改这个简单的图片。非屏蔽机制迅速在表面产生大的流函数值，其结果是共振效应更强。对流层PVB和对流层顶PVB之间存在类似的共振效应，对地面流函数放大产生负面影响。平流层对地面发展的影响可以忽略不计。在这里报告的所有情况下，由于传统的正常模式斜压不稳定的增长贡献或负或只有很少的表面发展的优化时间为两天。它需要至少四天的流量成为完全主导的正常模式的增长，从而确认有限时间的最佳扰动增长在许多方面从根本上不同于渐近正常模式斜压不稳定。
A detailed investigation has been performed of the role of the different growth mechanisms (resonance, potential vorticity unshielding, and normal-mode baroclinic instability) in the evolution of optimal perturbations constructed for a two-layer Eady model and a kinetic energy norm. The two-layer Eady model is obtained by replacing the conventional upper rigid lid by a simple but realistic stratosphere. To make an unambiguous discussion possible, generally applicable techniques have been developed. At the heart of these techniques lies a description of the linear dynamics in terms of a variable number of potential vorticity building blocks (PVBs), which are zonally wavelike, vertically localized sheets of potential vorticity. If the optimal perturbation is composed of only one PVB, the rapid surface cyclogenesis can be attributed to the growth of the surface PVB (the edge wave), which is excited by the tropospheric PVB via a linear resonance effect. If the optimal perturbation is constructed using multiple PVBs, this simple picture is modified only in the sense that PV unshielding dominates the surface amplification for a short time after initialization. The unshielding mechanism rapidly creates large streamfunction values at the surface, as a result of which the resonance effect is much stronger. A similar resonance effect between the tropospheric PVBs and the tropopause PVB acts negatively on the surface streamfunction amplification. The influence of the stratosphere to the surface development is negligible. In all cases reported here, the growth due to traditional normal-mode baroclinic instability contributes either negative or only little to the surface development up to the optimization time of two days. It takes at least four days for the flow to become fully dominated by normal-mode growth, thereby confirming that finite-time optimal perturbation growth differs in many aspects fundamentally from asymptotic normalmode baroclinic instability.